This invention concerns a variator of a continuously variable automatic transmission and in particular of a belt-drive transmission for motor vehicles.
A continuously variable automatic transmission usually consists, among others, of a starting unit, a forward/reverse travel, an intermediate shaft, differential, hydraulic and electronic control devices and a variator. The variator, in turn, usually comprises one primary and one secondary variator. In a variator according to the belt-drive principle, the variator is designed with cone pulleys disposed in pairs and provided with a torque-transmitting belt-drive element which rotates between both pairs of cone pulleys. In such a transmission, an actual ratio go is defined by the running radius of the belt-drive element which results from the actual axial position of the cone pulleys.
The axially fixed cone pulleys, each associated with an input and output shaft, are diagonally opposite each other. According to the prior art, as the belt-drive element is mostly used a pushing linked band or a chain, the pushing linked band having the advantage of not developing much noise.
In the prior art, the outlines of the cone pulleys and the flanks of the pushing links or the flanks of the belt-drive element customarily have straight outlines. In DE 42 30 605 is described an example of a sprocket chain with straight outlines for continuously variable automatic transmissions. This already known chain consists of light, long, thick bolts and bearings having smooth, cylindrical surfaces and wedge-shaped, friction-resistant side surfaces with flattened medium marginal surfaces made of plastic material reinforced with fiber glass of high resistance to pressure or of steel pipe with lateral wedge bodies of plastic material, the same as of two wide, outer, flexible plastic bands reinforced with fiber glass with high tensile strength and two inner, wide, elastic, thin steel bands.
An example of a continuously variable automatic transmission according to the prior art having a pushing linked band with straight outlines in the contact zone pushing link element/cone pulley has been described in xe2x80x9cG. Lechner and H. Naunheimer, Vehicle Transmissions, Springer Editing House 1994, page 332.xe2x80x9d
However, there have been proposed other arched, domed outlines, especially in order to avoid edge support during operation.
DE 197 08 865 A1 describes in this context a sprocket chain for a continuously variable automatic transmission, the joints of which that connect the individual links of the chain are designed as pairs of rocking members wherein the friction surfaces of the cone pulleys and the front faces of the rocking members have a crown oriented against each other and corresponding to the arched course. Departing from a front face line situated parallel to the moving direction and lying 1:1 substantially on the radial height of the ratio position, the other radially outwardly adjacent front face lines, which describe the spatially curved front face, increasingly deviate at their intersection point with the rocking surface in direction to the associated cone pulley so that an edge support of the front faces of the rocking members is avoided. But this principle is applicable only to the case of a chain, since a pushing linked band consists of a plurality of small thin metal plates loosely lined upon two steel ring sets without such connecting joints. In addition DE 197 08 865 A1 discloses no connection between curved front faces of rocking joints and an angular misalignment of the chain variator.
The geometry of the outlines of the cone pulleys and the pushing link flanks of the variators known at present results in a geometric angular misalignment of the belt-drive element for almost all ratio values.
Therefrom particularly results an additional bending component of the steel rings of the pushing linked band used which reduces the service life thereof.
Accordingly, the problem on which this invention is based is to indicate a method for deducing the outlines of the cone pulleys and pushing link flanks of a variator of a continuously variable belt-drive transmission having a pushing linked band as belt-drive element so as entirely to compensate the geometrically determined angular misalignment.
Accordingly, it is proposed to give to the fixed cone pulley of one side of the variator an arbitrarily curved outline, then to calculate via a crowned pushing link flank outline an appertaining pushing link displacement path and, knowing the displacement path, to deduce the pushing link displacement path to the other side of the variator so that the displacement path is free of angular misalignment.
The second cone pulley outline is then calculated via the already indicated crowned outline of the pushing link flank so that the outlines of the cone pulleys and pushing link flanks of the variator make possible an operation free of angular misalignment.
The pushing link flanks can be arbitrarily uniformly configured; this has the condition of sufficient angles of inclination on the upper and lower edges of the cone pulley outline.
It is obtained by the inventive method that the belt-drive element is operated for all ratios free of angular misalignment.
Besides, within the scope of the inventive method, the crown of the pushing link flanks is configured so that edge support of the pushing linked band is eliminated, according to the invention, the angle of inclination the upper edge of the pushing link flank is steeper than the angle of inclination on the contact point in the position of the variator OD on the primary side or LOW on the secondary side. In addition, the angle of inclination on the lower edge of the pushing link flank is flatter than the angle of inclination on the contact point in the position of the variator LOW on the primary side or OD on the secondary side. The distance between the uppermost contact point and the upper edge of the pushing link or the lowermost contact point and the lower edge of the pushing link is selected here so that the flattenings do not extend over the pushing link edges due to Hertz compression.
Between the limit contact points, the pushing link flanks can arbitrarily be uniformly configured. This procedure results in clear and calculable contact ratios without edge supports.
According to the invention, drainage data compulsory in crowned pushing link flanks are eliminated, since the compressions resulting from the crowned contact surface of the suction link elements are eliminated in the disk-contact element to the extent that it poses no problem to penetrate through the elastohydrodynamic oil film in order to prevent slipping.
It is possible, according to the invention, to take into account deformations of the parts so as to prevent, according to a characteristic field composed of torque and/or load cycle, the axial components of the deformation and the angular misalignment resulting therefrom.
The inventive method can be implemented in the production of the cone pulleys and pushing link elements without considerable extra expenditure. By using the method of substantially increased life service of the pushing linked band is additionally obtained.
The inventive construction generates increased compressions in the contact pushing link element/disk. But the compressions have less contact surfaces than in straight contact outlines so that the contact area is surrounded throughout its periphery by pushing link material, is supported on all sides and can deform without exceeding the admissible pressure widths.